1. Field of the Invention
The present invention relates to image forming apparatuses using an electrophotographic process, such as copiers, printers, and facsimiles. More particularly, the present invention relates to an image forming apparatus that can cool a member to be cooled disposed inside the apparatus with an airflow producing portion (cooling fan).
2. Description of Related Art
In image forming apparatuses such as copiers and printers, a heated roller fusing method is widely adopted as a method for fusing an unfused toner image to paper. In the heated roller fusing method, at least one of a pair of rollers forming a nip has a built-in heat source, and paper carrying an unfused toner image is passed through the nip formed between the pair of rollers heated by the heat source, whereby the toner image is fused to the paper. The heat generated by the heat source easily builds up in the image forming apparatus, causing a rise in temperature inside the image forming apparatus. This rise in temperature may affect formation of images. Furthermore, in a developing device, heat is generated, for example, in a sliding portion and blades of an agitator screw as the toner is agitated, unfavorably causing a rise in temperature of the developing device that supplies toner to an image supporting member.
The rise in temperature of the developing device may cause the toner to melt, lowering flowability of the toner and making the toner stick to the screw provided for conveying and agitating the toner. The toner stuck to the screw and eventually deposited thereon may drastically deprive the screw of its toner conveying capability. This adversely affects the toner image developed on the surface of the image supporting member, and results in the formation of an image of unsatisfactory quality on the paper.
To solve this problem, in JP-A-2002-006697, a heat generating portion inside the apparatus body is cooled with a cooling fan. A blowoff port of the cooling fan is connected to toner boxes (portions to be cooled) of developing devices for black, cyan, yellow, and magenta with four ducts provided therebetween. The air from the cooling fan is passed through the ducts and is then blown onto the toner boxes, thereby cooling the toner boxes.
However, this conventional technology has a following drawback. If a space between the blowoff port of the cooling fan and the toner boxes is narrow, it is impossible to provide four ducts. This makes it difficult to cool the toner boxes.
To overcome this drawback, in JP-A-2007-041562, there are provided four flexible tubes each having, at one end thereof, an air inlet portion at which they are connected to a cooling fan, and having, at the other end thereof, an air blowoff portion that is attached so as to face the bottom surface of the toner box. The air from the cooling fan is taken in, and is made to flow through the four flexible tubes from the front toward the rear of the toner boxes along the bottom surfaces thereof. With this structure, even when there is no space to provide the ducts, it is possible to cool the toner boxes.
However, this conventional technology has the following drawbacks. The air coming from the cooling fan and taken into the flexible tubes does not reach all the way to the rear of the toner boxes. As a result, the degree of temperature rise differs between the front and rear ends of the toner boxes. That is, although the rise in temperature can be prevented near the front end of the toner boxes, the temperature continues to rise near the rear end thereof. This unfavorably makes the toner inside the toner boxes less flowable. The toner boxes are not the only ones that will be affected. In a fusing unit, too, the heat generated by a heat source such as a built-in heater of a fusing roller is transferred to a nearby paper conveying portion. This transferred heat unfavorably distorts the image fused to the paper.